Washing or sterilizing by micro-nano bubbles is a method that uses only water, air, and additives of a trace quantity, offering a reduced environmental load. Due to this, such method has attracted attention as an alternative to a conventional method for washing or sterilizing that uses materials like detergents and chemicals. In addition, because of such method being highly safe, an application as a sterilization method for vegetables and foods has been studied. Conventional methods for generating micro-nano bubbles have been known in three fashions: the gas-liquid two-phase swirl flow method, the venturi tube method, and the pressure dissolution method. (For example, refer to Patent Literatures 1 and 2 for the gas-liquid two-phase swirl flow method and the pressure dissolution method.)
Such methods are however not satisfactory because the number of micro-nano bubbles generated by each of such methods is still not large enough. Although each of such conventional three methods can easily produce micro-bubble water, nucleating agents like base and magnesium must be added to the micro-nano water for generating a sufficient number of micro-nano bubbles. Addition of the nucleating agents has been a major obstacle in expansion of application to washing and sterilization of such as semiconductor devices and food. At present however, it is very difficult to generate a large amount of micro-nano bubbles using pure water.
Pumps of various types are employable as the driving pump in an apparatus that generates bubbles using water, air, and additives of a trace quantity. However, washing and sterilization of semiconductor devices and foods require that all the pertinent apparatus components including the driving pump should operate without causing metal contamination. For example, when devices such as semiconductor wafers are to be washed without metal contamination, all the wetted parts of pumps to be used in an apparatus for generating micro-nano bubbles should be made of those which do not generate any metal ions; and further, such pumps must operate stably at a discharge pressure of 0.3 to 0.6 MPa.
In consideration for these, the inventors of the present invention have proposed an apparatus that employs a compressed-air driven bellows-cylinder pump as a pump that feeds liquid without using rotating movements (Patent Literatures 3 and 4). All the wetted parts of the proposed pump are made of fluorine resin to avoid the feared metal contamination that will occur in a rotating type pump. To achieve the goal of performing a clean washing without the influence of contamination, technical development is desired on application of plastic by use of such as fluorine resin to all the related constituent units for generating micro-bubbles, including not only pumps but also nozzles.
{Patent Literature 1}
Laid-open patent application TOKKAI 2009-274045
{Patent Literature 2}
Laid-open patent application TOKKAI 2008-264771
{Patent Literature 3}
U.S. Pat. No. 4,547,451
{Patent Literature 4}
U.S. Pat. No. 4,924,907